75cc vs.65cc cylinder heads

[jptonks]

Hello all,

I am building up a 383 stroker from scratch. I am not using any of the major components from my existing engine. My goals are a fairly mild 430 hp/400 ft lbs torque, max 6000 rpm, 9.5 to 1 compression ratio, mild hydraulic roller cam, 6 speed T-56, and 17 in wheels.

Which aluminum cylinder heads should I select, 65cc or 75cc? I understand the cylinder head that I choose will dictate what kind of pistons are needed to achieve 9.5 to 1 cr. So if the combination of both sets of heads, pistons and gaskets yields
9.5 cr, why would I choose one over the other? I believe there is no significant difference in the cost for either combination.



Dr. John

[IMPALA MAN]

When I used to spec out engines I would purposely put 76 cc heads on an engine when possible and here is why. I would set the engine up with pistons that would not interfere with (hit) a 64 cc head. Therefore you know they won't interfere with (hit) a 76 cc head.
The pistons I chose would give me about 9 to 9.5 to 1 compression ratio with a 76 cc head. (Typically anything over 9.5 to 1 will not live on the street. (NOTE: If you run good gas say 93+ you can get by with more. Some will argue this point, however when I put a warranty on something I always tried to prepare for the worst like a buddy putting cheap fuel in or a fuel tank labeled wrong)
I am assuming you are balancing the rotating assembly (crank, rods, pistons, etc.) Say you go with 76cc heads and end up with 9.5 to 1 compression ratio. What you will end up with is a balanced 9.5 to 1 compression ratio engine. Say later you want to strictly race the car or sell the engine. All you need to do to raise the compression ratio is swap the heads. A simple swap. If you go another route like 64 cc heads to get 9.5 to 1 compression ratio and later want to bump it up, get ready to pay to tear down the engine and change out the pistons. When you change the pistons, your balance job goes by by. More cash. Racers used to do this all the time if they needed to run certain tracks that had different compression rules. So in summary, go for 76cc heads (or 75) and if you are going to street drive it, just play it safe, go no more than 9.5 to 1 and save yourself having to post a thread later on this forum asking how to fix the results of detonation.

[SShep71]

I dont know about doing 76cc heads, I would go for something in the middle and allow the ability to change the SCR a tiny bit by changing out head gaskets. You typically have a compressed thickness range of .027 - .061 head gasket thickness. Which allows about a .5 bump from lowest or a .5 drop from highest. This is a good option when you are going to worry about pinging and other compression related problems. Also a $100 set of head gaskets is alot cheaper than a head swap. You have to decide are you going to start your build with the rotating assy, or are you gonna start your build around the block. If you start your build around the rotating assy then you need to decide the pistons first. The target SCR and the pistons will give you the requirements for the gaskets and heads. If you start your build around the heads then the target SCR and the heads will give you the requirements for the piston dimensions. Some say to start with teh heads first, some say to start with the pistons fisrt. I have heard arguements either way. Its what are you comfortable with. You are missing a few important specs for determining CR. You also need to have your deck height figured out and your compression height determined. I have to disagree with IMPALA MAN about the streetability of the 9.5 CR. There are several well known steet machines out there running a near 11:1 CR with no problems. Its all in what you want out of it and what you are comfortable with doing. Is this going to be a SBC or LS based engine.

[jptonks]

SShep71,

I was tending toward a SBC engine, not an LS engine. I am old school and do not like the looks of the LS engines. I like to clearly see high end valve covers and a carb (or two) on top.

I have not purchased anything yet; not the block, the crank or the pistons, but was getting ready to do so this summer. Since this is a fresh build up, I can buy a new Dart cast iron block or buy a remanufactured block from Summit Racing or someone else. A new Dart block might be overkill. I am pretty well settled on AFR 195 aluminum street heads and an appropriate Comp Cams hydraulic roller and a four barrel carb (maybe even dual quads just for show if I can make them work properly).

Having said all of the above, I am open to any parts combination recommendations from experienced builders. I want the engine in this 1969 Camaro to be dependable, fun to drive and relatively low maintence once it is assembled.

The car will be street driven only and is not a daily driver.

Thanks for your help.

Dr. John

[astroracer]

Check this out...
PACE Performance - GMP-24502609-3 - GM ZZ4 350CID Fully Assembled Engine with Polished Finish
355 horse, pump gas, Complete engine for less then 5200 dollars AND a 2 year, 50,000 mile warranty...
Swap the cam down the road to bump it up a bit...
You will not build one from scratch for this kind of money...

[SShep71]

DR John,
I dont want to be the one to push you in any direction. There are several different ways you can setup an LS to look. For what you are going to spend on the SBC setup you can build a great LS motor, with carbs and relocated coils. It would look alot like a SBC, it would just be fore efficient and more fun to drive. I would suggest you do some more research before you buy anything. If you really are that set on the old school SBC, and you have the funds I would suggest a Dart or similiar block to start. FOr what you are going to pay in machine shop fees to totally start with a slid foundation you are looking at (clean, magnaflux, bake, shot peen, burnish the lifter bores or install bronze bushing and hone to size, line hone (if it has 4 bolt caps already)/or/ install aftermarket caps (line bore and line hone), deck, bore with torque plate, hone with torque plate). All of this machine work is around 1-1250.00. I am not trying to scare you off, but this is all stuff that we did to a block that was determined to be used in a race setup or for someone that really wanted to start the right way. That is one of the reasons that a LS is light years ahead of the SBC. On the flip side of it, you can just buy a 350 SBC and do the stroker kit, slap some AFR heads on it and be done with it. At the end of the day it is going to some down to two things. How much are you willing to spend, and how much do you intend to make. To do a 383 from where you are at you are looking at a block, stroker kit, heads, valve train, etc etc etc. You will be putting a good amount into the engine just in parts alone. This is all just my .02 and I am SURE there are others out there that would do it totally different than me.

[GBNL]

Go with the 75cc and if you ever want more compression you can always mill them.

[Skip Fix]

Not sure on the SBC how they get the different cc-either a larger diameter chamber or a deeper one(how Pontiac heads are).

If the chamber is deeper it affects the short turn radius and generally decreases flow. Why many guys use the small chamber and a dish piston vs the large chamber and a flat top.

FWIW there is a 383 GM crate motor that comes with a warranty!

GM Parts Direct: 12498772 - ZZ383 CRATE ENGINE